Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/98

86 isopurpuric acid and picramic acid, but these have only a limited application in dyeing. Coralline, a dye in extensive use, yielding a variety of fine red shades, is obtained by heating together two parts of oxalic acid, three of carbolic acid, and four of sulphuric acid to a temperature of from 140 C. to 150 C. Peonine, or red coralline, is a product of coralline obtained by acting on it at a temperature of about 130 C. with a concentrated solution of ammonia. It yields on wool and silk a very rich durable Turkey-red- like shade. Aurine, or yellow coralline, is made by mixing together oxalic acid, carbolic acid and sulphuric acid, the same as for ordinary coralline, but the mixture is submitted to a less elevated temperature. It dyes fine yellow and orange shades on animal fibres. Phenicienne, or rothine, is a dye producing shades varying from a deep garnet red to a chamois colour, made by adding to carbolic acid a mixture of nitric and sulphuric acids. Fol s yellow is manufactured by heating to 100C. a mixture of five parts of carbolic acid and three of powdered arsenic acid. Besides these various other dyes having carbolic acid for their basis have been introduced and some of them are commercially established.  CARBON (symbol, C; atomic weight, 12) is one of the most important of the chemical elements. It occurs pure in the diamond, and nearly pure as graphite or plumbago ; it is a constituent of all animal and vegetable tissues and of coal ; and it also enters into the composition of many minerals, such as chalk and dolomite. Carbon is a solid substance, destitute of taste and odour; but it occurs in several modifications which exhibit very diverse physical properties. Thus, it is met with in the form of the diamond in transparent crystals belonging to the regular or cubical system, which conduct electricity but slowly ; and in the form of graphite in opaque crystals belonging to the hexagonal system, which conduct electricity nearly as well as the metals. The diamond is the hardest substance known, and has a relatively high specific gravity (3 33 to 3 55), but graphite is comparatively soft, producing a black shining streak when rubbed upon paper, and has a much lower specific gravity (2 15 to 2 35). In addition to these two crystalline modifications of carbon there are a number of varieties of non-crystalline or amorphous carbon, which, however, exhibit the greatest differences in physical properties. By heating to the high temperature afforded by a powerful galvanic battery, both the diamond and amorphous carbon are converted into graphite. In the electric arc carbon appears to be converted into vapour; but the temperature which is required to volatilize it is extremely high ; in fact, it has been calculated that the boiling- point of carbon is not less than about 7000 on the centigrade scale. Although the various allotropic modifications of carbon cannot always be satisfactorily distinguished by their physical properties, they may readily be distinguished, as Berthelot has shown, by their behaviour on treatment with certain oxidizing agents. The diamond is not affected thereby even after prolonged and reiterated treatment. The different varieties of amorphous carbon, however, are more or less readily entirely converted into humus-like substances, or &quot;humic acids,&quot; soluble in water, whereas the different varieties of graphite furnish &quot; graphitic oxides,&quot; which are insoluble in water, and especially characterized by the property of undergoing decomposition with deflagration when heated. The method of treatment adopted by Berthelot is as follows. The carbon in the form of an impalpable powder is mixed with the aid of a card with five times its weight of pulverized potassic chlorate, and this mixture is then formed little by little into a paste vi i fuming nitric acid. In performing these operations great care is necessary in order to avoid explosions, and at most five grams of carbon should be taken. The mixture, con tained in a small open flask, is allowed to stand several hours, and is then heated for three or four days without interruption to a temperature not higher than 50 or 60 C. ; the mass is then diluted with water and washed by decanta- tion with tepid water. It is necessary as a rule to repeat this series of operations several times in order entirely to dissolve the amorphous carbons, or to convert the graphites into graphitic oxides. Berthelot has examined a very large number of varieties of carbon in this manner with the following results. The carbon of wood charcoal, animal charcoal, coke, the so-called metallic carbon obtained by decomposing hydrocarbons by passing their vapours through a red-hot tube, gas-retort carbon, and various specimens of anthracite from different sources, all dissolved entirely with more or less readiness when treated in the above manner; lamp black, however, furnished a small amount of graphitic oxide. The amorphous carbon of the meteorite of Cranbourne (Australia) furnished a graphitic oxide identical with that obtained by similarly treating graphite from cast-iron, -but the carbon of the Orgueil meteorite was entirely soluble. The carbon of the Greenland meteoric rock discovered by Nordenskiold also dissolved entirely with the exception of a very in significant residue. Berthelot also examined the action of various agents on carbon, and finds that heat alone is without influence ; that is to say, the graphites are not changed into amorphous carbon, or the amorphous carbons into graphite, when heated to whiteness in an atmosphere of hydrogen or of chlorine. When, however, a pencil of gas-retort carbon is inflamed in an atmosphere of oxygen, and then as soon as the point is fully incandescent plunged into water, the part which has been heated contains a small quantity of graphite. On examining the pencils of carbon employed in producing the electric light it was found that the spongy mass of carbon collected on the negative pole contained a large proportion of graphite, but that only traces were present in the pencil employed as positive pole, which appears to indicate that it is necessary for the carbon to undergo volatilization in order that it may be converted into graphite. The graphite thus produced is not identical with that contained in cast-iron, nor with natural plumbago-; the same variety of graphite is produced, however, when the diamond is heated in the electric arc. The carbon separated from the various hydrocarbons by heat alone consists entirely of amorphous carbon, but that obtained on decomposing marsh gas by the electric spark contains a small quantity of graphite, and the carbon resulting from the decomposition of perchloride of carbon and bisulphide of carbon at a red heat contains a considerable proportion of graphite ; that resulting from the decomposition of cyanogen by the electric spark contains only traces of graphite. The specific heats of the several modifications of carbon also differ considerably ; that is to say, the amounts of heat required to raise equal weights through the same number of degrees of temperature are different. The diamond has the lowest, and amorphous carbon the highest specific heat; or to raise the temperature of a given weight of the diamond from the temperature a to the temperature I will require less heat than to raise the temperature of the same weight of amorphous carbon from the temperature a to b. Graphite.—Graphite is found native near Travancore in Ceylon, and near Moreton Bay in Australia, in several parts of the United States, in South Siberia, and in Germany, principally at Griessbach near Passau, always in rocks 